There are many perspectives on what development means and what causes underdevelopment. Todaro defines development as improving living standards, self-esteem, and freedom of choice in a multidimensional process. Marxist views emphasize modes of production while dependency theories see underdevelopment resulting from unequal international relationships that benefit wealthy countries. Popular development theories stress local diversity and emphasize bottom-up solutions over top-down approaches. No single theory can fully explain underdevelopment due to countries' heterogeneity, so development must be understood through an array of changing internal and external interactions over time and place.